The evolution of communication technologies continues to drive user preferences in the manner of access to networks. Wireless networks, especially for voice communications, now provide coverage in most areas of the industrialized world. Indeed, wireless voice communications are becoming a preferred method in many instances because of their convenience. In certain situations, it may even be less expensive to use a wireless telephone. For example, wireless phone service may actually be less expensive than bringing a second wired telephone into a home, or in remote areas.
At the same time, demand for data communication services and in particular demand for reliable high speed access to the Internet is also growing. This demand is growing so fast that local exchange carriers (LECs) are concerned that the demand will cause their networks to fall. It is expected that as time goes on, at least some of this demand will eventually shift to the wireless side, especially with the popularity of laptop computers, personal digital assistants, and other portable computing devices increases.
At the present time, there are difficulties integrating available wireless data systems with existing computer network infrastructure. To provide coverage to an area requires planning of various network components, as well as obtaining necessary licensing to access the airwaves from government authorities. In particular, not only must wireless modulation schemes be chosen from among the myriad of possibilities, including analog modulation standards such as AMPS, TACS and NMT, but also the emerging digital standards, including Time Division Multiple Access (TDMA) schemes such as Global System for Module (GSM) communications, and Code Division Multiple Access (CDMA). In addition, site locations for base station equipment must be chosen and acquired. Additional engineering is often required to determine proper tower heights, effective radiated power levels, and assignment of a frequency plan to an area within which wireless service is desired.
Although it provides almost ubiquitous coverage, the existing cellular voice infrastructure has been very expensive to build-out. Therefore, the most common method of using the cellular infrastructure to send data is quite analogous to how computers presently use wired telephones. In particular, digital data signals are first formatted by modern equipment to generate audio tones in the same manner as used for the wireline network. The audio tones are then fed to cellular voice transceiving equipment which modulates these tones according to the interface scheme in use. For example, an input data stream such as produced by a computer is first modulated to generate frequency shift keyed (FSK) signals at audio frequencies. The FSK audio signal is then modulated using, for example, the IS-95B standard for CDMA modulation such as is prevalent in the United States. This modulation scheme impresses a pair of codes on a given radio frequency signal including a pseudorandom noise (PN) spreading code and a orthogonal code to define multiple traffic channels.
It is also possible to use separate networks built specifically for data services such as so-called Cellular Packet Data (CDPD) networks. However, CDPD coverage is not nearly as ubiquitous as the coverage presently provided for cellular voice communications. This is most likely because the build-out of a CDPD network requires all of the costs associated with building out a separate network, including planning of base station sites, obtaining licensing, acquiring such sites and engineering their tower heights and radiated powers and frequency planning.
As mentioned above, the most popular communication scheme for voice cellular networks at the present time is based upon CDMA modulation. These standards dictate a radio frequency (RF) channel bandwidth of 1.2288 megahertz (MHz). Therefore, RF system planning engineers and component industries have standardized their products based upon this particular channel bandwidth, and these networks have been built out with radio equipment, site locations, tower heights, and frequency plans that assume this channel spacing.
Unfortunately, these CDMA standards also specify other parameters for the communication which are not optimized for data traffic. These include the soft hand-off processing needed to transfer control of a call from one base station to another with the cooperation of the subscriber unit. The requirements reduce overall system capacity since individual users may be communicating with two or more base stations at any given time.
Furthermore, existing CDMA protocols for wireless service assume that connections are to be maintained for the duration of a call. This is quite unlike the typical Internet connection which is quite irregular in its actual demand for information. For example, after requesting a Web page, the typical Internet user then expects a relatively large amount of data to be downloaded. However, the user then spends many seconds or even minutes viewing the Web page before additional information needs to be transmitted.
Briefly, present invention is a system for wireless data transmission that uses a channel bandwidth, channel separation, and radio frequency power spectrum which are compatible with existing deployments of wireless voice networks. However, the wireless data protocol specifies digital coding, modulation, channel use allocation, and power control schemes that are optimized for data communications. Thus, the transmitted waveforms, although appearing to be of a different format when viewed from a time domain perspective are, in general, compatible from a frequency domain perspective with existing cellular networks.
As a result, a data communication system utilizing this wireless data protocol has the same appearance from a radio frequency network planning perspective as a standard cellular system. Thus, from a service provider""s point of view, an optimized data service can be deployed using the same base station locations, tower heights, cell sites, and cell radii, as well as frequency reuse plans that were already developed for existing voice networks. However, from the perspective of the Internet service provider and the user, the system is optimized for data transmission.